This invention relates to the application of carbon nanotubes on agglomerates of ore fines to increase their mechanical strength. The present invention also refers to a process for the preparation of ore agglomerates having enhanced mechanical strength and to an agglomerate product having carbon nanotubes.
Nowadays, nanotechnology embodies several research areas, mainly engineering, chemistry, physics and biology. Various innovative products based on nanometric scale are already commercialized in the worldwide market. The carbon nanotubes technology is currently one of the hottest topics investigated by many research teams in the world due to their excellent mechanical, electrical and thermal properties. These special properties are due to the combination of the dimension and structure of the nanotubes. They are crystalline structures which have a cylindrical geometry with nanometric diameter composed only by carbon atoms. The possibilities of the use of the carbon nanotubes are countless, and the applications which are mainly explored nowadays are related to reinforcement of materials. Based on this scenario of possibilities, the present invention refers to the application of carbon nanotubes aiming to increase the mechanical strength of agglomerate products.
The physical strength of ore agglomerate products is one of the main quality requirements by metallurgical reactors and has a direct impact on the productivity and costs of the process. The carbon nanotubes technology opens a wide range of possibilities for application on the agglomeration routes of ore fines, working as a composite net which provides the agglomerate products, among other characteristics, high mechanical strength.
The state-of-the-art presents various technologies of cold agglomeration of ores. These technologies are based on the agglomeration of ore fines using binding agents such as cement, mortar, organic binders and carbonated residues. Associated to these binding agents, several additives are present to accelerate the agglomerated cure and improve their physical properties. Several patents show agglomeration technology for industrial residue applied in steelmaking and metallurgical industry using, among other additives, liquid sodium silicate. However, the application of carbon nanotubes as reinforcement for the silicate matrix aiming to increase the mechanical strength of agglomerated products has not been reported.
Document US2002152839 describes shaped bodies containing particulate iron materials, such as cast pellets, briquettes and alike, with sufficient strength to withstand temperatures of up to at least 1000° C. They can be obtained using a fully hydrated high-alumina cement as the binder. The strength of the pellets at elevated temperatures can be further enhanced by adding small amounts of bentonite, silica fume or other suitable supplementary cementing materials, and super plasticizer.
Document US2005061207 describes self-reducing, cold-bonded pellets that comprise iron ore concentrate, carbonaceous reducing agent, and finely divided Portland cement clinker with special requirements as binder. The components are combined together to form a mixture. Pellets are produced when the mixture is placed into a balling disc or rotating drum and water is added.
The present invention minimizes some of the problems on the production of agglomerates such as: the need of high addition of binding agents; low mechanical strength of agglomerates produced by cold routes; high generation of fines by transport and handling; high generation of fines by thermal chock; and contamination by undesirable elements derived from certain binding agents. The current invention minimizes the need of dosing various types of binding agents, does not add any new contaminants (except the carbon which is consider to benefit the agglomerate), increases significantly the mechanical strength of the agglomerate, reduces the generation of fines by transportation and handling, and allows the use of this product in reactors which need burden with high strength.
Table below compares the present invention with the conventional technology route, highlighting the main differences:
Conventional TechnologiesPresent inventionLow mechanical strengthFast cure with drying between 150 and200° C.Composition with severalOnly one or two binding agentsbinding agentsProcesses with higher energeticProcess with lower energetic costcostsHigh cost of the binding agentsModerate costBinding agents with variousOnly SiO2, Na2O and Ccontaminants (residues)Low strength if in contact withModerate strength in case of contactwaterwith waterLow mechanical strength at highHigh mechanical strength at hightemperaturestemperaturesThere are no evidences ofProduct produced from 100% oftechnology which uses 100% ofnatural pellet feed (without millingpellet feed without millingprocess) or with milling (when desired)